FIG. 10 shows a relevant prior art optical card 101. FIG. 9 shows the actual structure of such a card. In these FIGS. 9 and 10, display symbols 3 constitute the logo and other information which is entered on a base layer 2. A light-absorbing printed layer 4, which consists of a paint having low reflectivity in the wavelength region of the light used to record and reproduce data, is painted onto the base layer 2. Layer 5, on which data are recorded optically, is laminated onto the light-absorbing printed layer 4 by means of film 6. Transparent layer 7 and protective layer 8 are laminated, in that order, so as to cover the entire surface of base layer 2. The prior art optical card 101 is thus completed.
To record data on the above-described optical card 101, a light beam is modulated in a manner corresponding to the symbols to be recorded. This light beam is trained on the recording layer 5, causing pitting on that layer.
To reproduce, or play back, the data from optical card 101, a light beam is aimed at the pits on recording layer 5. The light is diffracted by the pits, and the resulting modulated optical signals are detected by a photodetector (not pictured).
Layer 5 on the prior art optical card 101 has a large recording surface. This makes it difficult to check the area where visible data, consisting of characters, images, and the like, are stored on the card. To address this problem, it has been suggested that visible data such as characters, images (a photo of the cardholder's face, etc.) and the like be entered on the back of optical card 101. However, this scheme leaves open the possibility that the data might be obliterated by being rubbed off and new data being forged in their place.
One solution to prevent forgery or alteration of the visible data would be to emboss this data on the surface of the optical card, thereby displaying such data as the identification number or the account number, as is done on standard credit cards or cash cards. However, this causes the card to have a non-uniform thickness, which makes it difficult for the card to be registered in the correct position in the recording and reproducing device.
Another solution is to record the identification number or account number image data on the recording layer 5, instead of that data being visible, so as to prevent forgery or alteration. However, this scheme results in the space available on layer 5 being substantially reduced. This is because the amount of space required, especially for image data, is prodigious. Furthermore, if a reproducing device is not available there is no way to verify that image data stored on layer 5.